U.S. Pat. No. 3,888,956 describes a method of producing metal granules. The method of this patent is widely used, particularly for the production of crude iron, ferro nickel, ferro chromium, etc. The method has also been used for the granulation of ferro silicon. However, certain problems are involved in the latter application. One of these problems is due to the fact that silicon has a comparatively low density. Moreover, during the solidification, pores are formed in the ferro silicon granules, which further reduce the effect of gravity upon the granules. The granules therefore sink comparatively slowly through the water, with the result that the water at the surface of the water is heated more than in the case when granulating heavier metals and more homogeneous granules, respectively. Further, the heat energy concentration in silicon is very high as compared to many other metals and alloys. The enthalpy per unit of weight of silicon is for example 2.3 times as high as that of iron. A granulation rate of 1000 kg/min of silicon thus, in terms of the amount of heat energy that has been drawn off, corresponds to the granulation of 2300 kg iron/min.
The combination of the low sinking rate and the high enthalpy of silicon and ferro silicon gives rise to very high heat concentrations and the formation of steam in the surface layer of the water when using the described granulation technique. This problem cannot be solved by increasing the intake of cooling water into the water tank, and even heavy circulation of the water will only give a minimal improvement. Therefore, in order to be able to produce granules with desired shapes and sizes, and also to prevent the risk of stream explosions, it is necessary to operate with a granulation rate which in many respects is undesirably low for the granulation of silicon, ferro silicon and the like.